The present invention relates to a scrolling method and apparatus in which a partial area of information stored in a frame memory is displayed on the display screen of a display device, and in which an operator moves the area presented as a display on the display screen through scrolling.
The scrolling of display data, particularly a system capable of smooth scrolling, has heretofore been discussed in a book entitled "Computer Graphics" written by J. D. FOLEY/A. VAN DAM, pp. 505-507. Here, a technique called the "refresh buffer conversion" is employed. With this technique, parts of a pattern stored in a refresh buffer (also called a "frame memory") are repeatedly converted into view frames and displayed on the screen of a display device, while the displayed parts (called "windows" of the refresh buffer or frame memory) are accessed in succession, whereby the pattern is scrolled.
An example of a screen display in the case where map information is successively scrolled using the prior-art system is shown in FIG. 12, in which display 121 shows a displayed state before the scrolling, and displayed states are presented as indicated by 122.fwdarw.123.fwdarw.124.fwdarw.125 during scrolling. The displayed state 126 is established after the scrolling completed.
In the prior-art system, all of the data in the frames of data stored in the frame memory are scrolled. Therefore, when the pattern has a large amount of data which is scrolled at high speed, the successively displayed states become confused and are difficult to see. Another problem is that, since the afterimage of the last frame of a pattern of data remaining on the face of a cathode-ray tube lies over a new frame of the pattern of data, the display tends to flicker and data in the pattern to be found through the scrolling operation is difficult to recognize.
Particularly, in case of displaying and scrolling a portion of an extensive drawing, the scrolling speed of the system must be increased in order to enhance the pattern retrieval capability of the search operation. In such cases, the above-mentioned problems are enhanced.
There has been another prior-art system, which is designed to facilitate the retrieval of a desired picture in such a way that the whole view of a pattern of data is presented on a part of the screen of a display, and an area of the pattern being indicated is denoted by a square or other mark in the overall view. This system, however, has the problem that, when the amount of data forming the pattern is large, the overall view becomes too small to easily recognize the details of the pattern.